So unfortunately, people will always try to game the system. In a game where there is but one winner, ESPECIALLY in a format where there are more than 2 people, no rule set is going to be perfect enough for it to just work.
So, with that disclaimer out of the way, the reason I said "If you'd get beat up in middle school for playing this" is not because these cards go against the card list rules, it's because they don't fit the vibe of B2 (most of the time. There are exceptions, like Buster Sword in a Cloud deck because of course Cloud has the Buster Sword, people can swallow that idea).
How would I clarify B2? I wouldn't. Each store is going to have its own B2 "meta." In some, there's one guy who always plays Glacial Chasm but plays it in a "fair" way (no tutoring for it, no ways to bring it back), so grabbing a few targeted land destruction cards are understandable because you want to deal with Glacial Chasm Jerry, and it just so happens to be blowing up the Voltron player's Rogue's Passage this game, that's fine. In other store metas, everyone plays super greedy mana bases, so if they see ONE targeted land destruction spell you're banished to B3 hell for the rest of that deck's lifetime.
Online with random people is where things get interesting, I think. That is where you can maybe formalize a bracket system much more cleanly than having to juggle it with in-person play. Thankfully, I think this problem is already kind of solved for me, using Canadian Highlander's Points system, ideally combined with our current Bracket system. I'd set a point value to each card, and say "Hey bracket 1 is 0 points, bracket 2 is X points, bracket 3 is Y points, and brackets 4 and 5 are unlimited points. Here's a list of cards that you cannot play below bracket 4 (even though they might be under your point value), and generally we try to avoid a million tutors and MLD in bracket 2."
So, like, Rhystic Study might be 5 points, and maybe the Bracket 2 limit is 5 points. You can run Rhystic Study, but that's all your points!
This would also let you put 1 point on The Buster Sword or 2 points on Burgeoning or whatever that isn't crazy all the time, but can be crazy in the right deck